1. Field of the Invention:
The invention relates to a scintillation camera apparatus, and more particularly, to a timing control circuit for analog-to-digital converters in the scintillation camera.
2. Description of the Prior Art
A scintillation camera apparatus is extensively known as an apparatus for administering radio isotopes in an object under medical examination and causing a scintillation detector to detect radiation (gamma rays) emitted from radio isotopes selectively concentrated in a specific internal organ, thereby performing medical diagnosis.
A known scintillation camera apparatus of this type includes three signal processing circuits. These signal processing circuits have functions for independently processing X- and Y-positional signals, representing two-dimensional x- and y-coordinate position data, and an energy signal (i.e., an energy signal of incident photons) at a position specified by x and y. These three signals are generated by the scintillation detector. Each signal processing circuit includes a sample and hold circuit for performing sampling and holding, and an A/D converter for converting a sampled analog signal to digital data.
These independent signal processing circuits independently process three different signals, i.e., the X-positional signal, the Y-positional signal and the Z (energy) signal. The operation timings of these three signal processing circuits are substantially identical. Therefore, changes, or fluctuations in drive currents flowing between the ground line and lines connected to the respective sample and holding circuits and A/D converters in the respective signal processing circuits are different from each other. The following drawbacks are thus introduced.
When a plurality of signal processing systems are simultaneously driven, noise periodically appears in the resultant image along the X-Y direction, thus adversely affecting clinical diagnosis.
Problems caused by the differential linearity error in A/D converters are generally present in conventional scintillation cameras. In addition, the noise problems described above are also introduced.
As for the latter problems, a problem caused by the A/D converter itself and a problem caused by interference between a plurality of signal processing systems including sample and hold means and series-connected A/D converting means are recognized.
It is an object of the present invention to provide a scintillation camera apparatus which can reduce adverse effects of interference, particularly between A/D converters in the respective signal processing channels, and prevent noises to be superimposed on the image, thereby producing an image for high-precision diagnosis.